A hot rolling train for rolling metal strip generally consists of a roughing train, a finishing train, and a coiling device. The metal strip firstly passes through the roughing train and then the finishing train and is finally supplied to the coiling device. In many cases generally at least in hot strip trains for rolling steel strip, furthermore a cooling line is provided. If it is provided, the cooling line is arranged downstream of the finishing train and upstream of the coiling device.
Narrow width tolerances are often specified for the rolling of the metal strip. Maintaining these width tolerances is an important quality feature. Actively influencing the width of the metal strip therefore generates an economic utility.
The width of the metal strip is influenced both in the roughing train and also in the finishing train and also on the way to the coiling device. In some cases, this influencing is actively performed.
Thus, for example, a method is known from the technical article “Development of Automatic Width Control System for Hot Strip Finishing Mills” by M. Nakayama et al., Proceedings of the Third International Conference on Technology of Plasticity, Kyoto, Jul. 1/6, 1990, vol. II, pages 791 to 796, in which a width measurement is performed after multiple (but not all) rolling stands of the finishing train. Using all provided width measurements, the missing width measured values are estimated by means of a model. A compensation for width deviations is performed by the calculation and switching on of an additional strip tension for each loop lifter controller.
Performing a pilot control for the width deviations is known from the technical article “Automatische Breitenregelung in der Warmbandstraβe Borlänge der SSAB Tunnplat [automatic width regulation in the hot strip train Borlänge of SSAB Tunnplat]” by Harald Natusch et al., stahl and eisen 122 (2002), issue 11, pages 93 to 100. The width in the finishing train is ascertained in a manner supported by a model. A measurement of the width is performed before and after the roughing train and after the finishing train.
Disclosed in “Automatische Breitenregelung in der Warmbandstraβe Borlânge der SSAB Tunnplåt” by Harald Natusch et al., is an integrated width control concept (“ein integriertes Breitenregelungskonzept”, page 95, left col., last paragraph). This concept comprises (see FIG. 4) an edger E1, a measurement system, and sensors for monitoring the material position to derive the width of the rolled product along its length in the roughing mill (R1, R2), the finishing mill (F1-F6) and downstream of the finishing mill and furthermore algorithms and strategies for controlling the width of the rolled stock.
Essential Measurement of the Width is Done at:
Entry width at Edger E1, width of transfer bar downstream of R2, measurement of final strip width downstream of F6. Measured width data are considered by a level 2 process control (“PSC”), page 96, paragraph “Messwertverarbeitung”) of the roughing mill. The measured width data are assigned to specific positions of the rolled strip (rolled stock).
Detecting the width of the metal strip in each case after the second and after the last rolling stand of a finishing train is known from the technical article “Automatic width control system using interstand tension in hot strip finishing mill” by Y. Hoshi et al., La Revue de Metallurgie-CIT, November 1996, pages 1413 to 1420. The tension between the first and the second rolling stands is regulated by means of the former measurement. The tensions between the third and the last rolling stand are regulated by means of the latter measurement.
Detecting a variable which is characteristic for the mass flow between each two rolling stands and, building on the detected variable, setting the strip tension between the two rolling stands, in order to reduce a width change, is known from DE 103 38 470 B4.
A method for regulating the width in a rolling train having at least two rolling stands, through which the metal strip passes in succession, is known from DE 198 51 053 A1. In this method, the width is detected after the last rolling stand passes through. The tension between the two rolling stands is regulated to influence the width of the metal strip.
A method for regulating the strip width during the finish rolling of hot strip in a multi-stand rolling train is known from EP 0 375 095 B1. In this method, the strip width is measured before the next-to-last stand and after the last stand. A width regulation using pilot control is performed. The strip tension before the last rolling stand of the rolling train is used as the control variable.
A width model for a finishing train is known from the technical article “Strip width variation behavior and its mathematical model in hot strip finishing mills” by Atsushi Ishii et al., Proceedings of The 7th International Conference on Steel Rolling 1998, Chiba, Japan, pages 93 to 98. Width influences in the rolling gap, for example, a relative strip profile change, a roller bend, a compressed length, and the intake-side and outlet-side tension are taken into consideration. Furthermore, width influences in the region between two rolling stands are taken into consideration, for example, the temperature, the tension prevailing in the metal strip, the yield strength, the strip temperature, and the duration.
A simplified width model is derived building on a width model based on finite elements in the technical article “Direct Width Control Systems Based on Width Prediction Models in Hot Strip Mill” by Cheol Jae Park et al., ISIJ International, vol. (2007), issue 1, pages 105 to 113. The simplified width model is supplemented using a neuronal network. It models the width in the finishing train as a function of the intake-side tension in the metal strip, the present width, the thickness reduction, the compressed length, and the dimensional change resistance.
The methods of the prior art already cause the actual width of the metal strip to approximate the target width. The methods often only function inadequately, however. In addition, in a hot strip train without coil box, the temperature distribution is often uneven viewed over the length of the metal strip, which in turn results in an uneven widening of the metal strip in the finishing train.